Sum Frequency Generation
Differential-Frequency Generation
Optical Parametric Generation
Phase Matching
Conversion Efficiency
Angle Tilting
Optimum Crystal Cut
Crystal Size
Brewster's angle
Handle A NLO Crystal
w1 - w2 = w3 (or 1/l1 -1/l2 = 1/l3 in wavelength)
It mixs one high energy photon and one low energy photon into another low energy photon.
For example: